Drilling, preparing for extraction and extraction of hydrocarbons from wells require awareness of location, condition or other information from the bottom and other intermediate points in the well. Some of such data may be provided by listening to sound traveling to the surface, but sounds from deep wells often do not reach the surface or are so attenuated as to be inaudible at the surface. Other signals or forms of data transfer likewise may not reach the surface.
Signals can be transmitted from a point in a well to the surface or another location on electrical or optical fiber cable, but in some situations such alternatives are prohibitively expensive or otherwise impractical or impossible.